1. Field of the Invention
The present invention relates to an intake manifold for a vehicle, including a plurality of branch pipes each of which is commonly connected at one end thereof to a surge tank and each of which has such a shape that is bent at substantially 90 degrees as a projected figure on a vertical plane, said branch pipes being arranged in parallel to one another in a horizontal direction, and an engine mounting flange which is connected commonly with the other end of each of the branch pipes, and in particular, to an improvement in a welded and joined structure in an intake manifold for a vehicle, having a pair of joining members made of synthetic resin and welded to each other, as well as to a process for producing an intake manifold for a vehicle, having an improved welded and joined structure.
2. Description of the Related Art
Such an intake manifold for a vehicle is already known, for example, from Publication W097/15755 and the like.
It is required that each of joint zones of an intake manifold for a vehicle, which is comprised of a plurality of joining members made of a synthetic resin welded together, have a joining strength sufficient to withstand an internal pressure. Moreover, it is required that a sufficient joining strength and rigidity be maintained at joint zones in the vicinity of an engine mounting flange in consideration of the disposition of a fuel rail and the like at a location near the flange.
On the other hand, it is a conventional widely employed practice to establish a welding margin substantially equally over the entire length of a joining line, when joining members made of a synthetic resin are to be welded to each other. Particularly, it is already known, for example, from European Patent Publication No. EP-0568560B1 and Japanese Patent Application Laid-open No.5-177712 and the like that a joining line having not only a plane surface perpendicular to the pressing direction during welding but also an inclined portion and a curved portion, enables the welding time to be shortened to thereby enhance the efficiency.
Therefore, an intake manifold for a vehicle has been made, including a plurality of branch pipes each of which is commonly connected at one end thereof to a surge tank and each of which has such a shape that is bent at substantially 90 degrees as a projected figure on a vertical plane, said branch pipes being arranged in parallel to one another in a horizontal direction, and an engine mounting flange which is connected commonly with the other ends of the branch pipes, in which a first joining member made of a synthetic resin and integrally provided with the engine mounting flange to constitute a portion of each of the branch pipes and a second joining member made of a synthetic resin and constituting the remaining portion of each branch pipe are welded to each other along a joining line extending in a loop and having an inclined portion disposed substantially half around each of the branch pipe in the vicinity of the engine mounting flange. However, the joining strength at the inclined portion of the joining line has been lower than that of other zones, and a required joining strength has not been obtained.
This is assumed to have been caused by no effective reinforcing backup being given to the inclined portion of the joining line at the time of welding. More specifically, since the inclined portion is disposed substantially half around the branch pipe so as to be inclined with respect to the pressing direction for pressing the joining members against each other at the time of welding, the arrangement is such that a pipe portion previously included in the first joining member to form the entire inner periphery of an intake passage and a part of the inclined portion are superposed one on another. Therefore, in pressing the first and second joining members against each other, it is difficult for a die to receive a portion of the first joining member corresponding to the inclined portion.
The present invention has been accomplished with such circumstance in view, and it is an object of the present invention to provide an intake manifold for a vehicle, wherein a reduction in joining strength of the portion in the vicinity of the engine mounting flange can be prevented, as well as a process for producing such an intake manifold.
To achieve the above object, according to a first feature of the present invention, there is provided an intake manifold for a vehicle, comprising a plurality of branch pipes each of which is commonly connected at one end thereof to a surge tank and each of which has such a shape that a projected figure on a vertical plane is bent at substantially 90 degrees and which are arranged in parallel to one another in a horizontal direction, an engine mounting flange which is connected commonly to the other ends of the branch pipes, a first joining member made of a synthetic resin being integrally provided with the engine mounting flange and which constituting a portion of each of the branch pipes, and a second joining member made of a synthetic resin and constituting remaining portions of the branch pipes, the first and second joining members being welded to each other along a joining line which extends in a loop and has inclined portions disposed substantially half around said branch pipes in such a manner that they are inclined with respect to a pressing direction for pressing the joining members against each other at the time of welding, wherein among welding margins set in at least one of said first and second joining members along the joining line before welding, a welding margin in the pressing direction for zones corresponding to the inclined portions is set larger than that in the pressing direction for remaining zones excluding the inclined portions of the joining line.
With the first feature of the present invention, when the first and second joining members are to be pressed against and welded to each other, those portions of the first and second joining members which correspond to the inclined portions are brought into contact with each other before other portions. Even if each of the inclined portions is flexed due to no backup being provided to the inclined portion at its portion superposed on the pipe portion included in the first joining member in the pressing direction, the inclined portion is welded earlier or in a larger amount in correspondence to a difference in the welding margin in the pressing direction between the inclined portions and the other zones. Thus, when a predetermined amount of welding has been completed in the other zones, the amount of inclined portions welded is equal to or larger than the amount of other zones welded. As a result, the joining strength can be substantially uniform over the entire joining line, or the joining strength of the inclined portions can be larger than that of the other zones, thereby preventing a reduction in joining strength of the portion in the vicinity of the engine mounting flange.
According to a second feature of the present invention, the first joining member has pipe portions which are formed to be as portions of the branch pipes at locations on the side of the engine mounting flange, and the welding margin in the pressing direction for those zones of the inclined portions of the joining line which are superposed on the pipe portions in the pressing direction, is set larger than that in the remaining zones by an amount in a range of 10 to 25 %. With such arrangement, it is possible to reliably prevent a reduction in joining strength of the portion in the vicinity of the engine mounting flange and to avoid the time required for the welding being prolonged, and the amount of protruding molten resin n being increased. Specifically if the amount is lower than 10%, the amount of inclined portions flexed is larger than the difference between the joining margins and thus, an actual welding margin in the inclined portions is smaller than that in the other zones, resulting in a reduced joining strength of the portion in the vicinity of the engine mounting flange. If the amount exceeds 25%, not only the time required for the welding is prolonged wastefully, but also the amount of protruding molten resin produced by the welding is increased.
Alternatively, the welding margin for not only those portions of the inclined portions which are superposed on the pipe portion included in the first joining member in the pressing direction but also for the entire inclined portions may be set larger than that in the remaining zones by an amount of 10% to 25%. If the margin is set in this manner, the effect of enhancing the joining strength of the portion in the vicinity of the engine mounting flange can be further increased, and the variation in joining strength of the inclined portions can be suppressed.
According to a third feature of the present invention, in addition to the first or second feature, each of the inclined portions is inclined so that its level is lower at a position nearer to the engine mounting flange. With such arrangement, the second joining member can be supported over the entire joining line by a die on the side of the second joining member. On the other hand, it becomes difficult to support a portion of each of the inclined portions of the joining line by a die on the side of the fist joining member in order to prevent the interference with a fuel injector and a mounting portion for a fuel rail which are disposed above the engine mounting flange. However, to begin with, the present invention contemplates an intake manifold for a vehicle on the assumption that it is difficult to provide a reinforcing backup at a part of the inclined portions due to the superposition of the pipe portion included in the first joining member and the inclined portions, and the arrangement of the first or second feature makes up for the inability to support a part of the inclined portions, leading to no problem arising. Moreover, upon collision of the vehicle, the inclined portions hardly receive a damage from a member such as a fuel rail or the like disposed above the engine mounting flange.
According to a fourth feature of the present invention, there is provided a process for producing an intake manifold for a vehicle according to any one of the first to third features, comprising the steps of placing first and second joining members, so that they are sandwiched between a first die on the side of the first joining member and a second die on the side of the second joining member, with inner surfaces of their portions corresponding to the inclined portions being in non-restrained states, and pressing the first and second joining members against each other, and welding the first and second joining members in the pressed states in a vibrating manner along the joining line. With such producing process, taking into consideration that the arrangement of any of the first to third features makes it possible to avoid the reduction in joining strength of the inclined portions due to no effective reinforcing backup being given by the inclined portions of the joining line during welding, inner surfaces of those portions of the first and second joining members which correspond to the inclined portions are supported by dies and the like, thereby avoiding the complication of a mold structure to carry out vibration welding in a mold device having a simple structure as in the prior art.